In recent years, in order to achieve high breakdown voltage, low loss, and utilization of semiconductor devices under a high temperature environment, silicon carbide has begun to be adopted as a material for a semiconductor device. Silicon carbide is a wide band gap semiconductor having a band gap larger than that of silicon, which has been conventionally widely used as a material for semiconductor devices. Hence, by adopting silicon carbide as a material for a semiconductor device, the semiconductor device can have a high breakdown voltage, reduced on resistance, and the like. Further, the semiconductor device thus adopting silicon carbide as its material has characteristics less deteriorated even under a high temperature environment than those of a semiconductor device adopting silicon as its material, advantageously.
For example, Japanese Patent Laying-Open No. 2011-100928 (Patent Document 1) describes a method of forming an alignment mark in a silicon carbide substrate having an off direction of <11-20>. According to the method described in Japanese Patent Laying-Open No. 2011-100928, a trench is used as the alignment mark. The trench has an opening having a shape symmetrical relative to the off direction, and has a polygonal shape having an apex at a portion located in the most downstream side of the oft direction. Accordingly, the silicon carbide substrate and the mask can be aligned with each other with high precision.
Moreover, Japanese Patent Laying-Open No. 2013-65650 (Patent Document 2) describes a method for manufacturing a silicon carbide semiconductor device, including a step of aligning an optical mask with an original position by correcting an influence resulting from deformation of an alignment mark if the shape of the alignment mark is deformed. Accordingly, even when an off substrate is used, a photolithographic optical mask can be aligned precisely.
Furthermore, Japanese Patent Laying-Open No. 2009-170558 (Patent Document 3) describes that a first trench for forming a device and a second trench used as an alignment mark are formed such that the first trench has a solid angle larger than the solid angle of the second trench. Accordingly, the growth rate of the bottom portion of the first trench can be larger than the growth rate of the bottom portion of the second trench, whereby when the main surface of the substrate is planarized, a recess is formed in the portion having had the second trench formed therein and the recess can be used as an alignment mark.